I have my son's SX-636, it was working fine and then the left channel just quit. I have now given it a thorough DeOxit and cleaning...

Still no output from the left channel, it's dead.

nadude98

08-05-2009, 06:46 PM

I checked the Amplifier Adjustment on the left channel and I have -1.3v with an 8ohm dummy load and no input

nadude98

08-05-2009, 06:53 PM

Oh, it would probably be a good idea for me to at least recap the power supply and amp boards at least wouldn't it.

nadude98

08-05-2009, 08:09 PM

I did a search and found the transistor replacement on another thread. I replaced transistors Q 1,3,5,7 and 9. Left channel is now working again, however on the amp adjustment I cannot get down to 20mV on the left channel. The best I could achieve is 23mV. ????

Any thoughts?:D:scratch2:

markthefixer

08-05-2009, 11:20 PM

I did a search and found the transistor replacement on another thread. I replaced transistors Q 1,3,5,7 and 9. Left channel is now working again, however on the amp adjustment I cannot get down to 20mV on the left channel. The best I could achieve is 23mV. ????

WE need to read the base to base voltages at the output transistors at minimum bias on the pot on both channels, and at the correct bias point on the good channel. Red dmm probe on one base, the black probe on the other base of the output transistors for each channel.

Should be around 1 volt. The variations around 1 volt as you adjust the bias pot are critical.

I am assuming that you ARE talking about bias current.

I'm also surprised you didn't swap out the power output transistors.

nadude98

08-06-2009, 10:45 AM

I did not have output transisitors on hand, but I did have the rest. I will check those later today.

Thanks,

nadude98

08-06-2009, 01:22 PM

Ok, you are still running the original outputs?

WE need to read the base to base voltages at the output transistors at minimum bias on the pot on both channels, and at the correct bias point on the good channel. Red dmm probe on one base, the black probe on the other base of the output transistors for each channel.

Should be around 1 volt. The variations around 1 volt as you adjust the bias pot are critical.
1.11v right channel and 1.18v left channel and 1.16v with bias adjusted correctly on the right channel

I am assuming that you ARE talking about bias current.

I'm also surprised you didn't swap out the power output transistors.

If and when I do a cap order I will order outputs. It's just after ordering so many times I order quite a few extra of the transistors that seemed to be used a lot...:D

nadude98

08-07-2009, 11:16 PM

No Mas?

What could be causing the idle current to be so high I can't get it down to spec?

markthefixer

08-08-2009, 12:25 AM

No Mas?

What could be causing the idle current to be so high I can't get it down to spec?

The voltages are in the correct range, so there could be a fault with the power transistors. Too much leakage perhaps, maybe partially fried junctions.

Transistors of this type are cheap enough to just replace...

nadude98

08-08-2009, 01:55 AM

The voltages are in the correct range, so there could be a fault with the power transistors. Too much leakage perhaps, maybe partially fried junctions.

Transistors of this type are cheap enough to just replace...

Okay, is the list I have correct? Is there a recap list for the 636?

A little off the subject, I saw a Manual today that had schematics and circuit board layouts for all the Pioneer models of receiver, amps and shortwave receivers from the early 70's. How handy would something like that be? As far as receivers I noticed it had everything from the SX-424 to the SX-1010 plus the quads, just everything..... It was cool and looked almost brand new!